Clinton was in her hometown of Chappaqua, N.Y. on Monday and marched in a Memorial Day parade with her husband, former President Bill Clinton. Sanders stayed in California to walk in a parade and attend a Golden State Warriors basketball game.

The primary race in California could go either way, although a Clinton win there is not entirely necessary. As NBC points out, President Barack Obama lost California to Clinton in the 2008 primary election.

"It's going to be closer than we thought," former Los Angeles Mayor Antonio Villaraigosa told the Los Angeles Times. Villaraigosa is a Clinton supporter.

"Hillary's going to be the nominee, but California's the big prize, and obviously she'd like to go into the convention with a win in California."